Strong type alias?

[vlo...@gmail.com]

Is there any support for strong type aliasing? I see it on the roadmap but I'm guessing no progress has been done on that front?

The specific use-case I'm dealing with is time & wanting to ensure the correct units and epoch can be used (e.g. define a function taking a monotonic_clock::timepoint and return a strongly typed 64-bit integer nanoseconds that's typed to represent network time so that when the other side reads it it needs to reverse convert.

More advanced would be to be able to define a Vector3f data type that I know will only ever have 3 floats that I can reuse in a bunch of places without paying for the cost of it being a separate struct (.e.g it would take an "offset" field number & use up offset + N). So something like:

group@N Vector3f {

   x @N[0] :float;

   y @N[1] :float;

   z @N[2] :float;

}

struct MyAwesomeStruct {

    ...

    vec3 @10 :Vector3f@10;

    vec3 @12 :Vector3f@12;

}

The actual syntax that would make sense I have no opinion on. This is intended to just communicate what I would like the behaviour to look like. It would ideally actually be typed in C++ too rather than purely a convenience schema syntax.

[ku...@bertec.com]

I had something similar in mind, but didn't think of reusing the group syntax back them. Reusing the group syntax for that would probably

incur minimum mental and implementation overhead. It might even work without schema changes.

- Kuba

[Kenton Varda]

Hi Vitali,

What you propose looks pretty similar to what I've had in mind for a while for "inline structs".

I might do it more like:

    struct Vector3f inlineable {

      // `inlineable` keyword generates code that uses dynamic field offsets

      // from a table at runtime, thereby enabling inlining with varying layouts.

      x @0 :Float32;

      y @1 :Float32;

      z @2 :Float32;

    }

    struct MyAwesomeStruct {

      foo @[2..4] :Vector3f;

      // typical use: layout is like a group, but the type is Vector3f

      bar @[0..1,5] :Vector3f;

      // split use; useful when the inlined struct adds new fields.

      baz @[6] :Vector3f;

      // incomplete use; produces compiler warning like:

      //     Vector3f has been extended with two new fields; to use them you must assign two more numbers.

      qux @[7..9] :List(Float32);

      // inline list, always has 3 elements.

    }

Unfortunately I don't have any timeline for implementing this feature, and I do worry that it will be overcomplicated...

-Kenton

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[Vitali Lovich]

What about strong typedefs just for "primitives" like timestamps where implicit conversion is more of a concern than absolute optimization?

[Ian Denhardt]

+1.

As a data point: in the Haskell runtime library's RPC support, I ended
up manually defining newtype wrappers around Ids for Import/Export and
Question/Answer -- this is kinda sad since the schema actually already
define aliases, but the schema compiler doesn't convey this in any way
to the code generator plugin.

-Ian

Quoting Vitali Lovich (2019-09-16 16:27:01)

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